Once the object is suspended some empty space will appear in the loop because the upwards force will pull it away from the object. Being on the upper side the knot won't rest against a surface so it must not be a binding knot.
It would be good to see what you have in mind,
but a quick idea is to get your snugness with a
constrictor knot whose ends rise up into some
eye knot. Then you do NOT have any gap in your
snugness, you have a good grip on the object,
and ... it's all fairly easily done/undone.
Another, general tactic for snugness-gripping as you
seem to want is to have an eye knot that feeds its
eye-sides to either side into a structure like the
scaffold hitch --getting a quais 2:1 pull on a bight
and so snugging the surrounding material on the
object. At this moment, e.g., I have a piece of
webbing surrounding a protective bag on a large
bubblewrapped book, to carry. Hmmm, let me
paint the general idea as this:
1) small eye knot in one end, comes up on Side-A
about 3/4 to top of object;
2) piece runs from eye down beneath object and up
Side-B, where a mid-line eye knot is formed also about
3/4 of object height;
3) piece runs from this mid-line eye (to be an anchor
point) over top of object and down through first eye
qua sheave and now up long enough to be my handle [ <--"now", not "not" ]
and then down tied to the mid-line eye.
.:. Holding by the handle will put a sort of 2:1 pulling
on the Side-A eye, down through it and back over the
top and down, snugging my material to grip the object.
--kinda similar to my big Ikea bag which has on each
side both long and short straps :: put each long strap
across the top of stuff (I just salvaged foam paper,
bubblewrap, heavy plastic tarp, and newspaper (NYTimes))
and through the other side's small strap and now lift
by the long ends --they snug down across the top,
pulling sides towards each other, compressing my load
of *stuff*.
--dl*
====